CN108164819B

CN108164819B - Nanotube halloysite-diatomite-polymer micro-nano composite material and preparation method thereof

Info

Publication number: CN108164819B
Application number: CN201711434686.5A
Authority: CN
Inventors: 程志林; 赵亚荣; 朱爱萍; 刘赞
Original assignee: Yangzhou University
Current assignee: Yangzhou University
Priority date: 2017-12-26
Filing date: 2017-12-26
Publication date: 2020-08-25
Anticipated expiration: 2037-12-26
Also published as: CN108164819A

Abstract

The invention discloses a nanotube halloysite-diatomite-polymer micro-nano composite material and a preparation method thereof, wherein the micro-nano composite material is prepared by mixing a halloysite-diatomite mixture subjected to spray granulation with any one of polymer PP and PA6, then crushing at a high speed to prepare halloysite-diatomite-polymer micro-nano composite powder, and then extruding and forming by using double screws, wherein the tensile strength of the prepared composite material is increased by 12-16%, the relative elastic modulus of Young modulus is increased by 38-50%, the bending strength is increased by 20-46%, the notch impact strength is increased by 30-43%, and the Rockwell hardness is increased by 6-12%. The invention does not need surface modification, and realizes the performance enhancement of the polymer only by adjusting different proportions of the halloysite and the diatomite; the preparation process is simple, no environmental pollution is caused, mass production can be realized, and the cost is low; the mechanical property of the filled compound is comprehensively improved.

Description

Nanotube halloysite-diatomite-polymer micro-nano composite material and preparation method thereof

Technical Field

The invention belongs to the field of macromolecules, and relates to a preparation method of a halloysite-diatomite-polymer micro-nano composite material.

Background

The polymer nanocomposite is a novel material filled with a nano filler, and exhibits more excellent thermal and physical properties than conventional polymer materials. Polypropylene (PP and PA6) has become one of the thermoplastic polymers widely used in the fields of household goods, automobile parts, electronic packaging, etc., and has low processing cost and high crack resistance, but has very low crack propagation resistance and quite poor impact resistance particularly at low temperatures. Therefore, polymers are more likely to be used in combination with various nanofillers such as carbon nanotubes, layered silicates (montmorillonite) and nanoparticles (silica, graphite, calcium carbonate, etc.) and the like. When the inorganic additive is sufficiently dispersed in the polymer, the mechanical properties of the polymer can be improved.

Demori et al found that nonionic surfactant-based propoxylated and ethoxylated alkylphenols, along with their plasticizer, increased the dispersibility of HNTs (halloysite), and that the resulting nanocomposites exhibited an increase in Young's modulus without loss of impact strength and thermal properties [ AIP Conference Proceedings,2014,274:1593 ]. Ismail et al studied the effect of HNTs on PP composites and concluded that under a load of 2% HNTs, the composites exhibited 22% increased tensile strength with slightly reduced elongation at break but increased modulus and stiffness and improved thermal stability [ journal Vinyl & Additive Technology,2016,22:487-491 ]. Erdogan et al modified HNTs with silane coupling agent (gamma-Aminopropyltriethoxysilane (APTES)) filled PA6, and the yield strength, tensile strength and flexural strength of the nanocomposite were increased by 22%, 21% and 41%, respectively [ Polymer Composites,2014,35: 1350-.

The research results show that the halloysite is required to be subjected to surface modification for obtaining better performance when being filled into the polymer, and in addition, from the filling effect, although some performance indexes of the polymer are enhanced, other indexes are reduced, the whole preparation process is complex to operate and high in cost, and the risk of environmental pollution exists.

Disclosure of Invention

The invention aims to provide a preparation method of a halloysite-diatomite-polymer micro-nano composite material.

The technical solution for realizing the purpose of the invention is as follows:

a nanotube halloysite-diatomite-polymer micro-nano composite material is prepared by mixing a halloysite-diatomite mixture subjected to spray granulation with any one of powder of polymer PP and PA6, crushing at a high speed to prepare halloysite-diatomite-polymer micro-nano composite powder, and extruding and forming by a double screw.

Further, the mixture of halloysite and diatomite accounts for 5-8% of the total weight of the composite material.

Furthermore, the tensile strength of the composite material is increased by 12-16%, the relative elastic modulus of the Young modulus is increased by 38-50%, the bending strength is increased by 20-46%, the notch impact strength is increased by 30-43%, and the Rockwell hardness is increased by 6-12%.

The preparation method of the composite material comprises the following steps:

(1) sieving natural halloysite and diatomite powder by using a 100-plus-200-mesh sieve, then putting the two sieved powders into a container according to a certain proportion, pouring dry ice or liquid nitrogen with the volume 2-4 times of that of the powder, and then drying at the temperature of 100-plus-120 ℃ for 3-6 hours;

(2) adding 1mol/L sodium hydroxide solution into the dried filler according to the weight ratio of 1 (2-5), adjusting the pH value to 10-12, stirring the mixture at the temperature of 30-60 ℃, treating the mixture for 4-6 hours, filtering and washing the mixture to prepare suspension liquid with the solid content of 20-50 wt.%;

(3) granulating the suspension liquid in the step (2) by adopting spray drying, wherein the inlet temperature is 140-160 ℃; the outlet temperature is 70-80 ℃, and the pressure is 0.2-0.4 MPa;

(4) putting the spray-granulated halloysite-diatomite and polymer powder into a high-speed powder machine for processing for 1-3 hours, wherein the rotating speed of the powder machine is 1000-3000r/min, and preparing halloysite-diatomite-polymer micro-nano composite powder;

(5) preparing the micro-nano composite material powder in the step (4) into the nanotube halloysite-diatomite-polymer composite material by using a double-screw extruder, wherein the screw rotating speed of the extruder is 80-100r/min, the preheating temperature is 140-.

Further, in the step (1), the weight ratio of the halloysite to the diatomite is (1-6): (6-1).

Further, in the step (1), the diatomite is of a disc-shaped macroporous structure with the diameter of 4-6 microns, and the pore diameter of the macropores is 40-60 nanometers; the halloysite is a hollow tubular structure with a diameter of 50-80 nanometers and a length of 1-3 microns.

Further, in the step (3), the particle size of the spray-dried granules is 100-500 microns, preferably 100-300 microns.

Further, in the step (3), a two-fluid spray drying device is adopted for spray drying.

Further, in the step (4), the polymer is one of PP and PA 6.

Compared with the prior art, the invention has the advantages that: (1) halloysite and diatomite are used as natural mineral nano materials, so that the natural mineral nano materials are safe and environment-friendly, raw materials are easy to obtain, and the price is far lower than that of carbon nano tubes and carbon fibers; (2) the surface modification is not needed, the performance of the reinforced polymer is enhanced only by adjusting different proportions of the halloysite and the diatomite, and the preparation process is simple, has no environmental pollution, can be produced in large batch and has low cost. (4) The mechanical property of the filled compound is comprehensively improved.

Drawings

FIG. 1 is a cross-sectional profile of samples according to examples 2(A) and 5(B) of the present invention.

Detailed Description

Example 1

Sieving natural halloysite and diatomite powder by using a 100-mesh sieve, pouring liquid nitrogen with the volume 2 times that of the natural halloysite and the diatomite powder, drying the mixture in an oven at 110 ℃ for 4 hours, uniformly mixing 1 part by weight of halloysite and 6 parts by weight of diatomite by using a high-speed pulverizer at the rotating speed of 1000r/min, taking out the mixture, adding the mixture into 1mol/L sodium hydroxide solution with the weight 2 times that of the mixture, adjusting the pH value to 11, stirring the mixture at the temperature of 50 ℃ for 3 hours, filtering and cleaning the mixture for 5 times, adding distilled water, stirring and diluting the mixture into 40 wt.% of suspension liquid. Adjusting the inlet temperature of the spray drying equipment to 140 ℃; the outlet temperature was 80 ℃ and the pressure was 0.3MPa, and spray granulation was carried out to obtain an average particle size of 400 μm. And (3) taking 94 parts by weight of PP master batch, wherein the granulating body part is 6 parts by weight, pouring into a powder machine for processing for 1 hour at the rotating speed of 2000r/min, and finally preparing halloysite-diatomite-PP polymer micro-nano composite powder. Preparing the micro-nano composite material powder into a halloysite-diatomite-PP polymer composite material by using a double-screw extruder, wherein the rotating speed of a screw is 100r/min, the preheating temperature is 160 ℃, and the temperatures from a hopper to a die are respectively as follows: 150/200/200/220/220/220/220 ℃ and the mechanical properties of the samples are given in Table 1.

Example 2

Respectively sieving natural halloysite and diatomite powder by using a 100-mesh sieve, pouring dry ice with the volume 4 times that of the natural halloysite and diatomite powder into the sieve, drying the mixture in an oven at 120 ℃ for 6 hours, uniformly mixing 3 parts of halloysite and 3 parts of diatomite by using a high-speed pulverizer at the rotating speed of 1000r/min, adding the mixed mixture into 1mol/L sodium hydroxide solution with the weight 2 times that of the mixture, adjusting the pH value to 10, stirring the mixture at the temperature of 40 ℃, treating the mixture for 4 hours, filtering and cleaning the mixture for 3 times, adding distilled water, and stirring and diluting the mixture into 40 wt.% of suspension liquid. Adjusting the inlet temperature of the spray drying equipment to 150 ℃; the outlet temperature is 80 ℃, the pressure is 0.3MPa, spray granulation is carried out, and the average grain diameter of the granulated mixture is 300 microns. And taking 94 parts by weight of PP master batch, pouring 6 parts by weight of the granulation mixture into a powder machine for processing for 3 hours at the rotating speed of 1000r/min, and finally preparing halloysite-diatomite-PP micro-nano composite powder. Preparing the micro-nano composite material powder into a nanotube halloysite-diatomite-PP polymer composite material by using a double-screw extruder, wherein the rotating speed of a screw is 100r/min, the preheating temperature is 140 ℃, and the temperatures from a hopper to a die are respectively as follows: 140/200/200/220/220/220/220 ℃, the mechanical properties of the sample are shown in Table 1, and the photograph of the cross section thereof is shown in FIG. 1 (A).

Example 3

Sieving natural halloysite and halloysite powder by using a 200-mesh sieve, pouring liquid nitrogen with the volume 2 times that of the natural halloysite and halloysite powder into an oven, drying the mixture for 3 hours at 120 ℃, uniformly mixing 6 parts by weight of halloysite and 1 part by weight of diatomite by using a high-speed powder machine at the rotating speed of 1000r/min, taking out the mixture, adding the mixture into 1mol/L sodium hydroxide solution with the weight 3 times that of the mixture, adjusting the pH value to 10, stirring the mixture at the temperature of 40 ℃ for 4 hours, filtering and washing the mixture for 3 times, adding distilled water, and stirring and diluting the mixture into 30 wt.% of suspension. Adjusting the inlet temperature of the spray drying equipment to 145 ℃; the outlet temperature was 75 ℃ and the pressure was 0.2MPa, and spray granulation was carried out to obtain an average particle diameter of 300. mu.m. And taking 94 parts by weight of PP master batch, wherein the granulating part is 6 parts by weight, pouring into a powder machine for processing for 1 hour at the rotating speed of 2000r/min, and finally preparing the halloysite-diatomite-PP micro-nano composite powder. Preparing the micro-nano composite material powder into a halloysite-diatomite-PP polymer composite material by using a double-screw extruder, wherein the rotating speed of a screw is 100r/min, the preheating temperature is 160 ℃, and the temperatures from a hopper to a die are respectively as follows: 150/200/200/220/220/220/220 ℃ and the mechanical properties of the samples are given in Table 1.

Example 4

Sieving natural halloysite and diatomite powder by using a 100-mesh sieve, pouring dry ice with the volume 4 times that of the natural halloysite and diatomite powder into the sieve, drying the mixture in an oven at 100 ℃ for 3 hours, uniformly mixing 1 part by weight of halloysite and 6 parts by weight of diatomite by using a high-speed pulverizer at the rotating speed of 1000r/min, taking out the mixture, adding the mixture into 1mol/L sodium hydroxide solution with the weight 2 times that of the mixture, adjusting the pH value to 10, stirring the mixture at the temperature of 60 ℃ for 3 hours, filtering and cleaning the mixture for 3 times, adding distilled water, and stirring and diluting the mixture into 30 wt.% of suspension liquid. Adjusting the inlet temperature of the spray drying equipment to 140 ℃; the outlet temperature was 80 ℃ and the pressure was 0.3MPa, and spray granulation was carried out to obtain an average particle size of 400 μm. And (3) taking 94 parts by weight of PA6 master batch, taking 6 parts by weight of the granulation body, pouring into a powder machine for processing for 1 hour at the rotating speed of 2000r/min, and finally preparing halloysite-diatomite-PA 6 polymer micro-nano composite powder. Preparing halloysite-diatomite-PA 6 polymer composite material from micro-nano composite material powder by using a double-screw extruder, wherein the rotating speed of a screw is 100r/min, the preheating temperature is 160 ℃, and the temperatures from a hopper to a die are respectively as follows: 150/200/200/220/220/220/220 ℃ and the mechanical properties of the samples are given in Table 2.

Example 5

Respectively sieving natural halloysite and diatomite powder by using a 100-mesh sieve, pouring dry ice with the volume 4 times that of the natural halloysite and diatomite powder into the sieve, drying the mixture in an oven at 110 ℃ for 3 hours, respectively taking 5 parts by weight of halloysite and 1 part by weight of diatomite, uniformly mixing the mixture by using a high-speed pulverizer at the rotating speed of 1000r/min, taking out the mixture, adding the mixture into 1mol/L sodium hydroxide solution with the weight 3 times that of the mixture, adjusting the pH value to 11, stirring the mixture at the stirring temperature of 50 ℃ for 4 hours, filtering and cleaning the mixture for 3 times, adding distilled water, and stirring and diluting the mixture into 32 wt.% of suspension liquid. Adjusting the inlet temperature of the spray drying equipment to 160 ℃; the outlet temperature is 70 ℃, the pressure is 0.3MPa, spray granulation is carried out, and the average grain diameter of the granulated mixture is 200 microns. And (3) taking 95 parts by weight of PA6 master batch, taking 5 parts by weight of the granulation mixture, pouring into a powder machine for processing for 3 hours at the rotating speed of 1000r/min, and finally preparing halloysite-diatomite-PA 6 polymer micro-nano composite powder. Preparing the micro-nano composite material powder into a nanotube halloysite-diatomite-PA 6 composite material by using a double-screw extruder, wherein the rotating speed of a screw is 100r/min, the preheating temperature is 140 ℃, and the temperatures from a hopper to a die are respectively as follows: 140/200/200/220/220/220/220 ℃ and the mechanical properties of the sample are shown in Table 2, and the photograph of the cross section thereof is shown in FIG. 1 (B).

Example 6

Sieving natural halloysite and diatomite powder by using a 100-mesh sieve, pouring liquid nitrogen with the volume 3 times that of the natural halloysite and diatomite powder into the sieve, drying the mixture in an oven at 120 ℃ for 4 hours, uniformly mixing 6 parts by weight of halloysite and 1 part by weight of diatomite by using a high-speed pulverizer at the rotating speed of 1000r/min, taking out the mixture, adding the mixture into 1mol/L sodium hydroxide solution with the weight 3 times that of the mixture, adjusting the pH value to 11, stirring the mixture at the temperature of 60 ℃ for 6 hours, filtering and cleaning the mixture for 3 times, adding distilled water, and stirring and diluting the mixture into 36 wt.% of suspension liquid. Adjusting the inlet temperature of the spray drying equipment to 150 ℃; the outlet temperature was 75 ℃ and the pressure was 0.3MPa, and spray granulation was carried out to obtain an average particle diameter of 300. mu.m. And (3) taking 94 parts by weight of PA6 master batch, taking 6 parts by weight of the granulation body, pouring into a powder machine for processing for 1 hour at the rotating speed of 2000r/min, and finally preparing halloysite-diatomite-PA 6 micro-nano composite powder. Preparing halloysite-diatomite-PA 6 polymer composite material from micro-nano composite material powder by using a double-screw extruder, wherein the rotating speed of a screw is 100r/min, the preheating temperature is 140 ℃, and the temperatures from a hopper to a die are respectively as follows: 160/200/200/220/220/220/220 ℃ and the mechanical properties of the samples are given in Table 2.

Comparative example 1

Sieving diatomite powder by using a sieve of 100 meshes, pouring dry ice with the volume 2 times that of the diatomite powder, drying the mixture for 4 hours in an oven at 110 ℃, then adding the mixture into 1mol/L sodium hydroxide solution with the weight 2 times that of the mixture, adjusting the pH value to 11, stirring the mixture at 50 ℃, treating the mixture for 3 hours, filtering and washing the mixture for 5 times, adding distilled water, and stirring and diluting the mixture into 40 wt.% of suspension liquid. Adjusting the inlet temperature of the spray drying equipment to 140 ℃; the outlet temperature was 80 ℃ and the pressure was 0.3MPa, and spray granulation was carried out to obtain an average particle size of 400 μm. And (3) taking 94 parts of PP master batch, wherein the number of the granules is 6, pouring into a powder machine for processing for 1 hour at the rotating speed of 2000r/min, and finally preparing the diatomite-PP micro-nano composite powder. Preparing the micro-nano composite material powder into a nanotube halloysite-diatomite-polymer composite material by using a double-screw extruder, wherein the rotating speed of a screw is 100r/min, the preheating temperature is 160 ℃, and the temperatures from a hopper to a die are respectively as follows: 150/200/200/220/220/220/220 ℃ and the mechanical properties of the samples are given in Table 1.

Comparative example 2

Sieving halloysite powder with a 200-mesh sieve, pouring liquid nitrogen with the volume 2 times that of the halloysite powder, drying the halloysite powder in an oven at 120 ℃ for 3 hours, adding the halloysite powder into 1mol/L sodium hydroxide solution with the weight 3 times that of the halloysite powder, adjusting the pH value to 10, stirring the mixture at 40 ℃ for 4 hours, filtering and cleaning the mixture for 3 times, adding distilled water, and stirring and diluting the mixture into 30 wt.% of suspension liquid. Adjusting the inlet temperature of the spray drying equipment to 145 ℃; the outlet temperature was 75 ℃ and the pressure was 0.4MPa, and spray granulation was carried out to obtain an average particle diameter of 300. mu.m. And (3) taking 94 parts of PP master batch, wherein the number of the granules is 6, pouring into a powder machine for processing for 1 hour at the rotating speed of 1000r/min, and finally preparing halloysite-diatomite-PP micro-nano composite powder. Preparing the micro-nano composite material powder into a nanotube halloysite-polymer composite material by using a double-screw extruder, wherein the rotating speed of a screw is 100r/min, the preheating temperature is 160 ℃, and the temperatures from a hopper to a die are respectively as follows: 150/200/200/220/220/220/220 ℃ and the mechanical properties of the samples are given in Table 1.

Comparative example 3

Sieving diatomite powder by using a 200-mesh sieve, pouring dry ice with the volume being 3 times of that of the diatomite powder, drying the mixture for 3 hours in an oven at 100 ℃, then adding the mixture into 1mol/L sodium hydroxide solution with the weight being 4 times of that of the diatomite powder, adjusting the pH value to 10, stirring the mixture at 70 ℃, treating the mixture for 3 hours, filtering and washing the mixture for 5 times, adding distilled water, and stirring and diluting the mixture into 40 wt.% of suspension liquid. Adjusting the inlet temperature of the spray drying equipment to 130 ℃; the outlet temperature was 70 ℃ and the pressure was 0.2MPa, and spray granulation was carried out to obtain an average particle size of 500 μm. And (3) taking 94 parts of PA6 master batch, pouring 6 parts of the granules into a powder machine for processing for 1 hour at the rotating speed of 1000r/min, and finally preparing the diatomite-PA 6 micro-nano composite powder. Preparing the micro-nano composite material powder into a nanotube halloysite-diatomite-polymer composite material by using a double-screw extruder, wherein the rotating speed of a screw is 100r/min, the preheating temperature is 160 ℃, and the temperatures from a hopper to a die are respectively as follows: 150/200/200/220/220/220/220 ℃ and the mechanical properties of the samples are given in Table 2.

Comparative example 4

Sieving halloysite powder with a 100-mesh sieve, pouring liquid nitrogen with the volume 4 times that of the halloysite powder, drying the halloysite powder in an oven at 110 ℃ for 5 hours, adding the halloysite powder into 1mol/L sodium hydroxide solution with the weight 2 times that of the halloysite powder, adjusting the pH value to 9, stirring the mixture at 50 ℃ for 2 hours, filtering and cleaning the mixture for 3 times, adding distilled water, and stirring and diluting the mixture into 30 wt.% of suspension liquid. Adjusting the inlet temperature of the spray drying equipment to 145 ℃; the outlet temperature was 85 ℃ and the pressure was 0.1MPa, and spray granulation was carried out to obtain an average particle diameter of 400 μm. And (3) taking 94 parts of PA6 master batch, pouring 6 parts of the granules into a powder machine for processing for 1 hour at the rotating speed of 2000r/min, and finally preparing the halloysite-diatomite-PA 6 micro-nano composite powder. Preparing the micro-nano composite material powder into a nanotube halloysite-polymer composite material by using a double-screw extruder, wherein the rotating speed of a screw is 100r/min, the preheating temperature is 160 ℃, and the temperatures from a hopper to a die are respectively as follows: 150/200/200/220/220/220/220 ℃ and the mechanical properties of the samples are given in Table 1.

TABLE 1 mechanical Property table of halloysite-diatomite-PP micro-nano composite material

TABLE 2 mechanical property table of halloysite-diatomite-PA 6 micro-nano composite material

Note: (1) the tensile strength in the yield is measured, the speed of a parallel head of stretching is 100mm/min, the tensile strength, modulus and elongation at break of the composite material can be directly obtained from a recorded stress-strain curve, and a double-shovel type (bone-shaped sample) sample is adopted, wherein the length is 115mm, the width is 10.20mm, and the thickness is 4.24 mm; (2) relative modulus refers to the ratio of the young's modulus of the examples to the blank sample. Experimental bending strength was determined by a three-point bending test. The crosshead speed for the bending was 5mm/min, the span was 64mm, and the width and thickness of the bent specimens were about 10.20mm and 4.24 mm. (3) Notched impact specimen notched impact strength. Dimensional parameters of each sample were measured by a digital micrometer. At least five tests were run per sample, all data shown as mean and standard deviation) (5) rockwell hardness test procedure: the initial test force (large hand) is applied first, then the main test force (small hand) is applied, and then the material returns to the initial test force, using a specified R-type indenter, and the rockwell hardness of the material is expressed as the difference in sample depth under the test forces applied twice before and after the application of force. Measuring the hardness of the sample by using an XHRD-150 type Rockwell hardness tester; (6) data were averaged over 5 replicates.

Claims

1. The nanotube halloysite-diatomite-polymer micro-nano composite material is characterized in that a halloysite-diatomite mixture subjected to spray granulation is mixed with any one of powder of PP and PA6, the mixture is crushed at a high speed to prepare halloysite-diatomite-polymer micro-nano composite powder, and the halloysite-diatomite mixture accounts for 5-8% of the total weight of the composite material and is prepared by extrusion forming of double screws; the tensile strength of the composite material is increased by 12-16%, the relative elastic modulus of the Young modulus is increased by 38-50%, the bending strength is increased by 20-46%, the notch impact strength is increased by 30-43%, the Rockwell hardness is increased by 6-12%,

the preparation method comprises the following steps:

(1) sieving natural halloysite and diatomite powder according to a certain proportion, putting the sieved powder into a container, pouring dry ice or liquid nitrogen, and then drying the powder at the temperature of 100-;

(2) adding the filler dried in the step (1) into a sodium hydroxide solution, adjusting the pH =10-12, stirring the mixture at the temperature of 30-60 ℃, treating the mixture for 4-6 hours, filtering and washing the mixture to prepare a suspension liquid with the solid content of 20-50 wt.%;

(4) carrying out high-speed crushing treatment on the halloysite-diatomite and the polymer powder subjected to spray granulation for 1-3 hours to prepare halloysite-diatomite-polymer micro-nano composite powder;

2. The preparation method of the nanotube halloysite-diatomite-polymer micro-nano composite material is characterized by comprising the following steps:

3. The method of claim 2, wherein the natural halloysite and diatomaceous earth powders are sieved using a 100-200 mesh sieve.

4. The method of claim 2, wherein the dry ice or liquid nitrogen is 2 to 4 times the volume of the natural halloysite and diatomaceous earth powder.

5. The method of claim 2, wherein the weight ratio of natural halloysite to diatomaceous earth is (1-6): (6-1).

6. The method of claim 2, wherein the diatomaceous earth has a disk-like macroporous structure with a diameter of 4-6 μm, and a macropore diameter of 40-60 nm; the natural halloysite is a hollow tubular structure with a diameter of 50-80 nanometers and a length of 1-3 micrometers.

7. The method according to claim 2, wherein the filler dried in the step (1) is added to a 1mol/L sodium hydroxide solution in a weight ratio of 1 (2-5).

8. The method as claimed in claim 2, wherein the high-speed pulverizing process employs a high-speed pulverizer, and the rotation speed of the pulverizer is 1000-3000 r/min.